1. Field of the Invention
The present invention related generally to a muffler for an exhaust system in a combustion engine, such as an automotive internal combustion engine, gas turbine engine, external combustion engine and so forth. More specifically, the invention relates to an exhaust noise reductive resin muffler which can successfully reduce noise level to be created in the exhaust system without degrading exhaust performance and thus without degrading the engine performance.
2. Description of the Background Art
As is well known, a combustion engine, such as automotive internal combustion engine employs an exhaust system for exhausting an exhaust gas created by combustion of air/fuel mixture in an engine combustion chamber. The exhaust gas in the exhaust system pulsates due to variation of pressure in the engine combustion chamber according to engine cycle. Such pulsatile exhaust gas tends to cause pulsatile noise and exhaust stream noise. In order to suppress such pulsatile noise and stream noise, a muffler of silencer is employed in the exhaust system. The muffler or silencer in the engine exhaust system serves for suppressing pulsation of the exhaust gas and make the pressure of the exhaust gas uniform.
Generally, such muffler or silencer is made of a steel or the like. Such metal muffler comprises a metallic hollow muffler body defining an internal space to smoothing pulsating exhaust gas. However, since the peripheral wall of the metal muffler body is substantially rigid and have substantially no pressure absorbing characteristics. Therefore, various proposal in changing the internal design of the muffler have been presented for successfully reducing the exhaust noise level. In general, reduction of noise in the exhaust system by changing design of the internal structure of the muffler may encounter a problem such as increase of back pressure of the exhaust gas at the engine exhaust port or increase of flow resistance against the exhaust gas and consequently a drop in engine performance.
On the other hand, it would be possible to suppress exhaust noise by attaching noise insulative lining on the inner periphery of the muffler. As the noise insulative lining material, asbestos, glass-fiber and so forth can be used. However, such noise insulative lining may creates another problem of polution.